This application incorporates by reference Taiwanese application Serial No. 90102297, Filed Feb. 2, 2001.
1. Field of the Invention
The invention relates in general to an ink detector, and in particular, to an apparatus for measuring the amount of ink remaining in an ink tank.
2. Description of the Related Art
In recent years, the personal computer has become so popular that the peripheral computer products, such as the scanner, printer, digital camera, and MP3 player, have developed very rapidly, becoming popular also. For example, within several years, the printing technique advanced from dot matrix to ink-jet to color laser. The color laser printers produce high quality printout but are relatively expensive, and therefore they still are not an affordable option for most PC buyers. Most individuals who purchase a printer for general use want the flexibility that comes with having a color printer. The ink-jet printer therefore becomes the most popular type of printer sold today, because it is relatively inexpensive and capable of generating color images. The ink-jet printer generally uses a bubble jet or a piezoelectric print head that ejects microscopic dots of ink onto the paper to create an image. The ink is contained in an ink tank and the operation of the ink tank is described below, with reference to FIGS. 1A and 1B.
In FIG. 1A, the cross-sectional view of the ink tank is illustrated. The ink tank 100 comprises a casing 110 and a bag 115. The volume between the casing 110 and the bag 115 is filed with ink. When the ink is ejected, the volume of the ink within the casing 110 decreases and the pressure within the casing 110 also decreases. Due to the reduction in pressure, the ink fails to be ejected successfully. For ejecting the ink properly, the pressure within the casing 110 must be remained essentially constant. One way to solve this problem is to make use of the bag 115 to modulate the pressure within the casing 110. In practice, the bag 115 is made of a flexible material and is communicated with atmosphere via a vent 101 in the casing 110. Thus when the volume of the ink within the casing 110 decreases, the atmosphere enters the bag 115 via the vent 101. The pressure within the casing 110 becomes, and remains at, slightly less than 1 atm, since the capacity of the ink tank 100 is small. As the volume of ink gradually decreases, the bag 115 expands to maintain a balanced pressure in the tank 100. When ink is exhausted, the bag 115 is inflated to fill the tank 100, as shown in FIG. 1B. For the bag 115 to expand properly along the inner wall of the casing 110, a guide plate 125 can be placed under the bag 115 such that the bag 115 is dragged downward smoothly.
Under the aforementioned structure of the ink tank, ejection of the ink can be performed successfully, however, the actual amount of ink inside the ink tank is not known, which can be a great inconvenience for the user. Oftentimes, the user discovers that the printer fails to print because the ink is exhausted. Therefore, a method of estimating the volume of ink remaining in the ink tank has been developed. According to this method, the amount of ink in the ink tank is estimated by calculating the cumulative ejecting times, and the more the ejecting times, the less ink in the ink tank. Thus the user can be informed of the estimated ink amount, before starting a print job.
The ink measurement is estimated by algorithm and is susceptible to erroneous estimations if the algorithm is inaccurate. Thus, an inaccurate algorithm might estimate an ink tank to be exhausted when it is not. In this case, the printer may inaccurately give a warning of ink exhaustion, prompting the user to change the ink tank before proceeding with a print job. Then the user may unknowingly discard an ink tank that is still usable. From the buyer""s point of view, the ink tank can be costly, so the buyer would want to maximize the ink tank""s usage, and such an error caused by the inaccurate algorithm results in wasteful use of the ink tank and wasteful use of the buyer""s money.
It is therefore an object of the invention to provide an apparatus for measuring the amount of ink remaining in an ink tank by using a sensing module to accurately monitor the amount of ink.
The invention achieves the above-mentioned object by providing an apparatus for measuring the amount of ink remaining in an ink tank, wherein the apparatus comprises a sensing module and a detecting circuit. The sensing module comprises a fixed device connected to the casing of the ink tank and a movable device connected to the bag. When the ink volume decreases, the volume of the bag increases, such that the movable device moves with the bag as the volume of the bag changes. The detecting circuit is coupled with the sensing module so that the detecting circuit generates a corresponding detecting signal (detection signal), according to the variation in the relative position of the movable device and the fixed device; thereby, a measurement of the ink amount remaining in the tank can be obtained.
In addition, several fixed devices can be located on the casing. When the movable device moves as the volume of the bag changes, the movable device will be sequentially coupled with the fixed devices and generate different detection signals, and thereby, a measurement of the ink amount can be obtained.
Furthermore, the movable device connected to the bag can be coupled with an adjustable device connected to the casing. As the volume of the bag changes, the movable device adjusts the electrical property of the adjustable device. Then the detecting circuit, coupled with the adjustable device, will generate corresponding detection signals, according to the variation in the electrical property of the adjustable device; thereby, a measurement of the amount of ink remaining is obtained.